Cepheid variable star in galaxy M100

The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance, which turns out to be 56 million light-years from Earth. This image was taken on May 9, 1994.

Credit:

Dr. Wendy L. Freedman, Observatories of the Carnegie Institution of Washington, and NASA/ESA